beta, beta-dicyano-alpha-hydroxyvinyl organic acids



United States Patent Q AB-DICYANO-u-HYDROXYVINYL ORGANIC ACIDS-.5

William Joseph lvliddletom wilmington, Del., assignor to E. I. du Pont de'Nemours and Company,--Wil mington,

It isknown 'that many organic carboxylic acids are strong acids in awater-system; This is particularly true of those carboxylic acids which are in some way activated by the presence of a functional group other than carboxyl in the molecule. "A well-known example is trichloroaceticacid which is among the. strongest of the carboxylic acids(pKs'=1.1, Branch, G. E. K., and Calvin, M.,' TheTheory .of Organic Chemistry, Prentice-Hall, Inc., New York, 1946, page. 224). It is further known that there are some carboxyl-free organic compounds. which :are capable of dissociating as acids in a water systemibecausethey possess a hydrogenatom sufliciently activated by other structuresin the; molecule. 'Numerically, this is a'relatively minor group of organic acids" and one which has received little com-; mercial attention to date:- I f An object of the present invention is to provide a new class of organic acids and their salts." A..further object is to provide a process of preparing such acids. A still further object is to provide a new class of carboxylfree organic acids. Other objects will be apparentfrom the-description of theinvention tgiven hereinafter.-

The' above 1 objects are accomplished according to the present invention by hydrolyzinginalkaline medium. C-tricyanovinyl compounds. in:,whichthe Ct-tricyanovinylgroup is attached to a carbon of either. a S-membered N-heterocyclic or G-memberedcarbocyclic -rganic-'ring,- to yield the alkaline" salts of the corresponding beta beta-dicyano-alpha-hydroxyvinyl compounds --and-- then acidifying the alkalinemedium to precipitate the corresponding beta,beta-dicyano-alpha-hydroxyvinyl organic acids j 51:. v I i i Due to the strong acidity of the --OH group attached to the carbon doubly bonded to the dicyano carbon, these 'compou'nds' are' all acidsz They may or may not contain a carb'o'xyl (-COOH) group in addition. A preferred group of these acids are those in which the beta,beta-'dicyano-alpha-hydroxyvinyl radical sible that-these beta,beta=dicyano+alpha=hydroxyvinyl* compounds may'represent a taut'omeric mixture as indicated by the following equilibrium: 3

R(i3 -C R-t'i-b-H ON ..N M

I II

However, infrared spectral examination of the particulai compounds of. the present invention. gives strong evidence for a structureof form I and no detectable evidence for a structure of form II. The strong'acidity of the compounds of the. present invention is especially surprising ,sincethe known 1,1+dicyanoacetone (where R=methyl) is a weak acid which has been shownto;

exist only up to 3.3%..in the .enolicform I;

The invention. can "be carried .out by.digesting the C- tricyanovinyl compound ..with aqueous alkali, until ,it is converted to'the' alkali salt "of the corresponding beta, beta-dicyano-alpha-hydroxyvinyl compound as evidenced byobtaining a cleari aqueous solution. The free. beta, beta-dicyano-alpha-hydroxyvinyl compound is obtained, as a precipitate whenihe solution. is acidified. This process maybe illustrated by the following equation:

The C-tricyanovinyl compounds used as starting materials in the'present invention, are characterized by having the grouping*(-CN)2C=C(CN )C as distinguished from.

the N-tricyanovinyl compounds characterizedby having a grouping (CN)zC=C;(CN)N. These- C-tricyanovinylcompounds are prepared according to the disclosures in- U. S. applications Serial Nos. 382,857, now abandoned; 382,858; and 382,860, all filed/September 28, 19.53 in the name of'R..E. Heckert. 1

, The following examples in which all proportions are by weight-unless; otherwisestated;illustrate the prepara--.

tion of organicv acids-according to thepresent invention.

' stampie 1' Z-tricyanovinyl-l-methylpyrrole, 25 parts, is added to 277 parts of 10% aqueous sodium. hydroxide, and the:

mixtureis wa'rm'etL-gentlyfor .21or 3, minutes untilsolution is completen'; Thetilight -yellow ;solution of 'rtht; sodium salt of 2-(beta,beta-dicyano-alpha-hydroxyvinyl)- l-methylpyrrole is cooled and then acidified with hyd'rochloric acid. The white precipitate which forms is collectedon afilter, washed with water, and recrystallized two times from water to give 10 parts of 2-(beta,betadicyano-alpha:hydroxyvinyl)-1-methylpyrrole in the form of matted white needles, M. P. 158 C.159 C.

Anal.-Calcd. for C9H7N3O: C, 62.42; H, 4.07; N, 24.22; Neut. Equiv., 173.17. Found: C, 62.19, 62.09; H, 4.34, 4.38; N, 24.23, 24.08; Neut. Equiv., 170.3, 171.5.

The infrared absorption spectrum indicates an --OH at 2.9 microns but shows no absorption due to a carbonyl. The molecular extinction coetlicient at 315 millimicrons is"1'5,540. The ultraviolet absorption measurements on which the molecular extinction coetficient is based, were made on a Cary recording spectrophotometer built by the Applied Physics Corporation of Pasadena, California. The terms used are explained on page 4, Chemical Spectroscopy by W. R. Brode, John Wiley & Sons,..New .-.ork, 1939.

As further -confirmation of the identification of this product, 20 parts of the above 2-(beta,beta-dicyano-a1phahydroxyvinyl)-1-methylpyrrole is dissolved in 555 parts of 10% aqueous sodium hydroxide, and the solution is heated under reflux for 18 hours. The solution is cooled andwacidified. With hydrochloric acid. A white precipitate forms which is recrystallized from water. There is obtained 5 parts of 2-(beta-carbamyl-beta-cyano-alphahydroxyvinyl)-1-methylpyrrole in the form of white needles, M. P. 158 C.160 C.

Anal. Calcd.. for C9H9N3O2: C, 56.54; H, 4.75; N, 21.98; Neuf-..-.';eqi1iv., 191.18. Found: C, 56.29, 56.45; H, 4.71, 4.60; N, 22.05, 22.25; Neut. equiv., 195.2, 194.8,

Example II A solution of 40 parts of 4-tricyanovinyl-2,6-dimethylphenol in 1109 parts of 10% sodium hydroxide is warmed momentarily to 90 C. and then quickly cooled and acididentical with that of an authentic sample of ethyl p-(dimethylamino)benzoate.

Example IV ified with hydrochloric acid. The precipitate which forms A Solution of 50 Parts of y y y is collected on a filter, washed with water, and recrysaniline in 330 Parts of aquwlls Sodium hydfoxidc tallized from alcohol-water. There is obtained 20 parts and 79 Parts of ethanol is heated to boiling and then of 4-(beta,beta-dicyano-alpha-hydroxyvinyl)-2,6-dimeth- Cooled immediately in The Orange precipitate 0f ylphenol in the form of light pink matted needles, M. P. the Sodium Salt of b y P Y Y' 236 C 238 C, 10 vinyl)-N-methylaniline which forms is recrystallized sev Allal.-Calcd f C I-1 N 0 (3, 6713; H, 4 1; eral times from dilute sodium hydroxide. An aqueous 13.08; Neut. equiv., 214.22. Found: C, 66.93, 66.84; solution of this sodium salt is acidified with hydrochloric H, 4.74, 4.71; N, 13,10, 12,95; N m equiv 215,4, acid. The white precipitate which forms, is collected pK =2,55 Exam I" on a filter, washed with water, and recrystallized from p ethanol to give 4-(beta,beta-dicyano-alpha-hydroxyvinyl)- A SOIHROH P 58 Parts of 4'(trlcyanovmynjmN'dl N-methylaniline in the form of pale yellow crystals, M. methylaniline in 277 parts of 10% aqueous sodium hydroxide and 79 parts of ethanol is heated to reflux ternc for C11H9N3O: C 66.32. H N perature and then cooled immediately in ice. The orange- Found: C 6636 6636. H brown precipitate of the sodium salt of 4-(beta,beta- 2094. dicyano-alpha-hydroxyvinyl) -N,N-dimethylaniline which PKa: 3 3 5 separates, is recrystallized several times from dilute so- Example V diurn hydroxide, using charcoal for decoloration until A solution of 14 parts of 4-(tricyanovinyl)-2,6-dimeththe product is pale yellow (27 parts, 44%). Acidificaylaniline in 110 parts of 10% sodium hydroxide and tion of an aqueous solution of this material gives 4-(beta, 24 parts of ethanol is heated momentarily to boiling beta-dicyano-alpha-hydroxyvinyl)-N,N-dimethylaniline in and then quickly cooled in ice. An orange-yellow prethe form of pale yellow needles, M. P. 210 C.2l1 C cipitate of the sodium salt of 4-(beta,beta-dicyano-alpha- AnaL-Calcd. for C12H11N3O: C, 67.59; H, 5.70; N, hydroxyvinyl)-2,6-dimethylaniline forms. An aqueous 19.71. Found: C, 67.68, 67.57; H,'5.63, 5.33; N, 20.21, solution of this sodium salt is acidified, and the result- 20.16. ant white precipitate is collected on a filter, washed with pKa=2.26. water, and recrystallized from ethanol. There is ob- A solution of 20 parts of this 4-(beta,beta-dicyanotained 9.5 parts of 4-(beta,beta-dicyano-alpha-hydroxyalpha-hydroxyvinyl)-N,N-dimethylaniline in 590 parts of vinyl) -2,6-dimethylaniline in the form of colorless crysethanol saturated with hydrogen chloride is refluxed for tals, M. P. 300 C. 5 hours. The ammonium chloride which forms is re- AnaL-Calcd. for CmHuNsO: C, 67.59; H, 5.20; N, moved by filtration, and the filtrate is evaporated on a 19.71. Found: C, 67.50, 67.61; H, 5.36, 5.42; N, 19.50, steam cone to about its original volume and then 19.57. poured into cold 10% sodium hydroxide solution. The PKB:3.05. pale yellow precipitate which forms is collected on a filter Examples of other C-tricyanovinyl starting materials and recrystallized from ethyl alcohol. There is obtained and the beta,beta-dicyano-alpha-hydroxyvinyl compounds 18 parts of ethyl p-(dimethylamino)benzoate, M. P. 64 obtained from them according to the present invention, C.64.5 C. The infrared spectrum of this compound is are shown inthe following table.

Table I Starting Compound Product 0H Z-Trlcyanovmylpyrrole 6 N) l N H 2-(Bfi-dlcyano-a-hyd.roxy-vinyl)pyrrole OH 23=G(ON): 3 Trloyanovinyl 2,5-dimethylpyrrole U N- 1(P- cyanoethyl) -N-methyl-ptrioyano-vlnylani- N-butyl-N-(B-cyanoethyl)-p-tricyanovlnylanlllne-.

CH: N-(fl-cyanoethyD-N-methyl-p- ,B-dicyano-ahydroxyvinyDa asses.

stirri Compound Product N-phenyl-p-tricyano-vinylaniline N-phenyl-m-hydroxy-p-tricyanovinylaniline N-(p-trioyanovinyl-phenyl) ethanolam ine G-Tricyanovinyl-l,2,3,4-tetrahydro-quinoline.

2-1ricyanovinyl-d-rnethylphenol 2 (6,8 dicyano -a 2-Tricyanovinyl-4,6-dimethy1phenol N phenyl; m hydroxy p -(B,B dieyano a hydroxyvinyDaniline G-(AB-dicyano if-(ilrydroxyvinyl) -1,2,3,4-tetra.

Y g m hydroxy -vinyl) 4 methyl phenol 2-(fl,B-dicyano-a-hydroxy-vinyl) -4,6-dimethylphenol It will be understood that the above examples are merely illustrative and that the present invention broadly comprises hydrolyzing in alkaline medium a C-tricyanovinyl compound in which the C-tricyanovinyl group is attached to a carbon of either a 6-membered carbocyclic or 5-membered N-heterocyclic organic ring, to yield the salt of the corresponding beta,beta-dicyano-alpha-hydroxyvinyl compound and then acidifying the alkaline medium to precipitate the corresponding free beta,betadicyano-alpha-hydroxyvinyl acid, and in these new acids and the salts thereof.

The reaction of this invention is broadly applicable to any C-tricyanovinyl compound providing the C-tricyanovinyl group is attached to a carbon of either a 6-membered carbocyclic or 5-membered N-heterocyclic organic ring and, consequently, there can be obtained the corresponding free acid or salt thereof. The examples disclose numerous C-tricyanovinyl compounds of the type adapted for use in the present invention, and the corresponding acids formed.

The alkaline digestion step of the process of the present invention is readily carried out at ordinary temperatures. For more rapid completion of this step, the reaction may be carried out at a temperature within the range of C. to 100 C. Temperatures in excess of 100 C. may also be employed, provided a closed vessel is used which is capable of withstanding the autogthe process of the present invention.

enous pressures developed. There is ordinarily no ad vantage obtained by operating at temperatures in excess of 100 (3., and at any temperature above room tem perature care must be taken to stop heating the reactants as soon as the beta,beta-dicyano-alpha-hydroxyvinyl compound is obtained since prolonged heating with strong alkali may destroy it. Pressure is not critical. 7

A wide variety of alkaline materials can be used in For example, the hydroxides or the carbonates of the alkali and alkaline earth metals may be used. Other alkaline materials can be used, such as ammonia and amines, particularly the quaternary ammonium hydroxides. In general, any agent which is a good source of hydroxyl ions can be employed.

It is convenient to employ water as a liquid medium for carrying out the process of the present invention, but other liquid media can also be employed, such as aqueous solutions of water-miscible organic compounds,

such as alcohols and phenols. Alternatively, the alkaline hydrolysis reaction can be carried out in the absence of water if desired. For example, the C-tricyanovinyl compound can be digested with a solution of potassium hydroxide in ethyl alcohol and the resulting potassium salt of the beta,beta-dicyano-alpha-hydroxyvinyl compound can be converted to the free hydroxy compound by passing in anhydrous hydrogen chloride until the mixture has been acidified.

The compounds of the present invention possess unique utility as self-indicating acids for conducting acid-base titrations.

point of inflection of pH, characteristic of each of these products, at which there is a sharp shift from colorless.

to colored forms or vice versa. These shifts are visible by ordinary light when using the phenolic types, such as the color change which takes place at a pH of 5.75 in dilute aqueous solutions of 4-(beta,beta-dicyano-alphahydroxyvinyl) 2,6 dimethylphenol, the product from Example II. With the others, this color shift is readily observed by optical examination of the system under ultraviolet light. In this way the quantitative determination of an alkaline material can be readily made by titrating with one of the acids of the present invention. Such a titration permits improved accuracy by eliminating the side reaction necessary to produce the color change in an extraneous indicator.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims,

The invention claimed is:

1. A compound selected from the class consisting of beta,beta-dicyano-alpha-hydroxyvinyl organic acids and their salts, in which the alpha-carbon of the vinyl group is attached to a carbon of a ring selected from the group consisting of S-membered N-heterocyclic and 6-rnembered carbocyclic rings.

2. A compound selected from the class consistingof beta,beta-dicyano-alpha-hydroxyvinyl organic acids and their salts, in which the alphacarbon of the vinyl group is attached to a carbon of a pyrrole ring.

In the titration of aqueous systems contain-- ing the products of the present invention, there is a.

3. A compound selected from the class consisting of beta,beta-dicyano-alpha-hydroxyvinyl organic acids and their salts, in which the alpha-carbon of the vinyl group is attached to a carbon of a benzene ring.

4. Process of preparing a beta,beta-dicyano-alphahydroxyvinyl organic acid, which comprises hydrolyzing in alkaline medium a C-tricyanovinyl compound in which the C-tricyanovinyl group is attached to a carbon of a ring selected from the group consisting of 5-mernbered N-heterocyclic and 6-membered carbocyclic rings, to yield the alkaline salt of the corresponding beta,betadicyano-alpha-hydroxyvinyl compound and then acidifying said alkaline'medium to precipitate the corresponding free acid.

5. Process of preparing a beta,beta-dicyano-alphahydroxyvinyl organic acid, which comprises hydrolyzing in an aqueous alkaline medium at a temperature below 100 C. a C-tricyanovinyl compound in which the C-tricyanovinyl group, is attached to a carbon of a ring selected from the group consisting of S-membered N-heterocyclic and G-membered carbocyclic aromatic rings, to yield the alkaline salt of the corresponding beta,beta-dicyano-alpha-hydroxyvinyl compound and then acidifying said aqueous medium to precipitate the corresponding free acid.

6. A process as defined in claim 5 wherein the hydrolyzing is carried out by heating within the range of to C. and heating is stopped as soon as the C-tricyanovinyl compound is hydrolyzed.

References Cited in the file of this patent Beilstein Band X, 2nd supp., 4th ed., page 362. Beilstein Band X, main book, 4th ed., page 521. 

1. A COMPOUND SELECTED FROM THE CLASS CONSISTING OF BETA,BETA-DICYANO-ALPHA-HYDROXYVINYL ORGANIC ACIDS AND THEIR SALTS, IN WHICH THE ALPHA-CARBON OF THE VINYL GROUP IS ATTACHED TO A CARBON OF A RING SELECTED FROM THE GROUP CONSISTING OF 5-MEMBERED N-HETEROCYCLIC AND 6-MEMBERED CARBOCYCLIC RINGS. 